This document provides information about the solar system and its planets. It begins with an outline of chapter topics on the solar system, sun, stars and galaxies. The bulk of the document then describes each planet in our solar system from Mercury to Pluto. It notes key facts about their size, composition and features. It also briefly discusses the Kuiper Belt and reclassification of Pluto.

2. Astronomy
• Chapter Fifteen: The Solar System
• Chapter Sixteen: The Sun and the Stars
• Chapter Seventeen: Galaxies and the
Universe

3. Chapter Fifteen: The Solar System
• 15.1 The Solar System
• 15.2 The Planets

4. Investigation 15B
• How big are the planets relative to Earth?
The Sizes of the Planets

5. Space Travel
• Why should I come visit your planet?

7. 15.2 Mercury
• Mercury, the
closest planet
to the sun, is
the second
smallest (after
Pluto) in both
size and mass.

9. 15.2 Venus
• Venus appears as
the brightest planet in
the evening sky and
is the third brightest
observable object
(after the sun and
moon).

11. 15.2 Earth
• Earth is a small, rocky
planet with an
atmosphere that is made
of mostly nitrogen (78
percent N2) and oxygen
(21 percent O2).

13. 15.2 The Seasons
• The seasons are caused by the 23-degree tilt of Earth’s
axis of rotation relative to its orbit.

14. 15.2 The moon
• Earth’s single rocky
moon is about one-
quarter the diameter of
Earth.
• At a distance of 385,000
kilometers, the moon is
about 30 Earth
diameters away from
the planet, completing
one orbit every 29 days.

15. 15.2 Mars
• The fourth planet
out from the sun,
Mars appears as
a reddish point
of light in the
night sky.

17. 15.2 Jupiter
• The fifth planet out
from the sun, Jupiter
is by far the largest.
• Jupiter’s mass is
greater than the
combined mass of all
of the other planets.
• With 63 known
moons, Jupiter is like
a mini solar system.

19. 15.2 Saturn
• Saturn, at almost 10
times the size of
Earth, is the second
largest planet.
• The most striking
feature of Saturn is
its system of rings
and like Jupiter, has
many natural
satellites.

21. 15.2 Uranus
• The seventh planet
from the sun, Uranus
can barely be seen
without a good
telescope and was
not discovered until
1781.

22. 15.2 Neptune
• Neptune, the eighth
planet from the sun,
is the outermost of
the gas planets.
• It was discovered in
1846 and its
discovery almost
doubled the diameter
of the known solar
system because of
its great distance
from the sun.

24. 15.2 Pluto
• Pluto is a dwarf
planet, and most of
the time the farthest
from the sun.
• Discovered in 1930,
Pluto was named for
the Roman god of the
underworld.

26. 15.2 The far outer system
• Outside the orbit of Pluto is a region called the
Kuiper Belt.
• The Kuiper Belt stretches to 1,000 AU and is
believed to contain many asteroid-size and a
few Pluto-size objects.
• To avoid confusion, astronomers no longer
count Pluto as a planet.
• Instead, Pluto is grouped along with Sedna,
Xena, and similar distant bodies in the Kuiper
Belt Objects (or KBOs).

27. Astronomy Connection
Jupiter’s Volcanic Moon
• In December of 1995 the
Galileo spacecraft entered
into orbit around Jupiter.
• Io, Jupiter’s “pizza moon”, is
considered to be the most
volcanically active place in
the solar system.

28. Activity
• The plants and animals that live on Earth are
uniquely suited to Earth’s environment.
• In this activity, you will create an organism that
could live on another planet.
Alien Design

29. 15.2 The planets
• The eight major planets of our solar system
together contain 250 times the surface area of
Earth.
• This vast territory includes environments baked
by heat and radiation (Mercury) and far colder
than ice (Neptune).
• With a combined surface area 1,700 times the
size of North America, the planets are an
unexplored frontier full of discoveries waiting to
be made.